controlling method execution

[mic]

Is it possible to control method exectution using similiar mechanism as with
get/setatrribute special methods for attributes? I'd like to have every (or
some of ) method of class instance run common code defined outside the class
without making any explicit references to it.
To give an example, I'd like to prepare secure environment, in which users
could execute only methods that can be accessed by them. IMO the most
universal way to do it would be to run automatically authorisation routine
before every method execution.

Regards,

Michal

[anton muhin]

mic wrote:

Is it possible to control method exectution using similiar mechanism as with
get/setatrribute special methods for attributes? I'd like to have every (or
some of ) method of class instance run common code defined outside the class
without making any explicit references to it.
To give an example, I'd like to prepare secure environment, in which users
could execute only methods that can be accessed by them. IMO the most
universal way to do it would be to run automatically authorisation routine
before every method execution.

Regards,

Michal

Here comes my humble attempt:

import inspect
import new

def before():
print "before"

class WrapperMeta(type):
def __new__(cls, name, bases, attrs):
wrapped = {}
for n, v in attrs.iteritems():
if inspect.isfunction(v):
class Controled(object):
def __get__(self, obj, cls):
before()
return new.instancemethod(v, obj, cls)

wrapped[n] = Controled()
attrs.update(wrapped)
return super(WrapperMeta, cls).__new__(cls, name, bases, attrs)

class Controled(object):
__metaclass__ = WrapperMeta

class Test(Controled):
def method(self, x, y):
print 'Test.method(%s, %s)' % (x, y)

test = Test()
test.method(10, 11)

I hope gurus will suggest better approaches. However, I'm afraid that
metaclass approach cannot guarantee enough security: one can simple get
rid of metaclass to bypass the mechanism.

regards,
anton.

[anton muhin]

anton muhin wrote:

mic wrote:

Is it possible to control method exectution using similiar mechanism
as with
get/setatrribute special methods for attributes? I'd like to have
every (or
some of ) method of class instance run common code defined outside the
class
without making any explicit references to it.
To give an example, I'd like to prepare secure environment, in which
users
could execute only methods that can be accessed by them. IMO the most
universal way to do it would be to run automatically authorisation
routine
before every method execution.

Regards,

Michal

Here comes my humble attempt:

import inspect
import new

def before():
print "before"

class WrapperMeta(type):
def __new__(cls, name, bases, attrs):
wrapped = {}
for n, v in attrs.iteritems():
if inspect.isfunction(v):
class Controled(object):
def __get__(self, obj, cls):
before()
return new.instancemethod(v, obj, cls)

wrapped[n] = Controled()
attrs.update(wrapped)
return super(WrapperMeta, cls).__new__(cls, name, bases, attrs)

class Controled(object):
__metaclass__ = WrapperMeta

class Test(Controled):
def method(self, x, y):
print 'Test.method(%s, %s)' % (x, y)

test = Test()
test.method(10, 11)

I hope gurus will suggest better approaches. However, I'm afraid that
metaclass approach cannot guarantee enough security: one can simple get
rid of metaclass to bypass the mechanism.

regards,
anton.

A bug: before gets called on simple Test.method. Better solution:

import inspect
import new

def before():
print 'before'

def after():
print 'after'

class WrapperMeta(type):
def __new__(cls, name, bases, attrs):
wrapped = {}
for n, v in attrs.iteritems():
if inspect.isfunction(v):
def wrapper(self, *args, **kwargs):
before()
new.instancemethod(v, self, cls)(*args, **kwargs)
after()

wrapped[n] = wrapper
attrs.update(wrapped)
return super(WrapperMeta, cls).__new__(cls, name, bases, attrs)

class Controled(object):
__metaclass__ = WrapperMeta

class Test(Controled):
def method(self, x, y):
print 'Test.method(%s, %s)' % (x, y)

test = Test()
test.method(10, 11)
test.method

sorry,
anton.